1. Field of Invention
The present invention relates to retaining walls and, more particularly, to concrete retaining wall systems of the gravity wall and soil reinforcement type.
2. History of the Prior Art
Retaining walls have been used for centuries to establish earthen contours and prevent soil mass from moving into areas adjacent the wall. Such structures are often used near roads, bridges, highways and other areas of both pedestrian and vehicle traffic to control rock, dirt, debris, and sand adjacent thereto. Retaining walls are also used in construction to secure a region of soil for purposes of foundational support. The type of retaining wall obviously depends upon the particular application and the amount and type of soil mass being retained. For this reason, the material used in and the design for retaining walls typically change from application to application.
Retaining walls can be found in a variety of shapes, sizes and styles. The walls that are used in residential areas often incorporate rocks or wooden beams, such as railroad cross ties. In certain situations, select cross ties are turned orthogonally into the soil mass (called "dead men") to secure the retaining wall. Commercial structures along highways, bridges and the like conventionally incorporate more complex pre-cast concrete configurations with elaborate securement systems. These concrete assemblies generally present a substantially planar face, which may be of considerable height and behind which soil or rock is secured in volumes that can generate larger loads against the retaining wall. In most instances, the concrete face is secured by a number of securement members which are carefully designed relative to the structural load associated therewith and which extend deeply into the soil mass. Such securement members are conventional in retaining wall technology and are used to prevent the retaining wall from moving or breaking as a result of static loads or movement of the soil mass.
Retaining wall designs date back into technological antiquity. Even early retaining walls had some anchoring technique, such as the "dead men" referenced above. These anchors are designed to carry some of the weight of the soil behind the retaining wall and resist the overturning moment of the soil against the wall itself. This rather basic structural loading technique is also seen in bookends, where the weight of the book upon a first horizontal, of two orthogonal members, prevents the upstanding vertical member from overturning by the transverse force of the book. By utilizing this basic structural theory in retaining walls, a myriad of retaining wall designs and assembly systems have been developed and the materials utilized have evolved into complex concrete structures.
Subsequent wall systems formed of concrete were constructed with forms assembled at the retaining wall site. The advent of the pre-cast system of concrete construction antiquated some of these designs because less excavation and traffic interruption resulted from the use of pre-cast technology. This is particularly true with the expansive highway systems of today, where retaining walls are used around and against the sides of the highway which must be kept open. With such technology, highway expansion can stay within permitted right-of-ways; traffic congestion is reduced and the environmental effect of the highway can be minimized in parks and other environmentally sensitive areas.
Today, retaining wall systems utilize sophisticated applications of civil engineering. The various members may be specifically designed for particular applications, pre-cast, delivered to the retaining wall site, and installed in a configuration that is much less expensive than pour in situ techniques. Much of the concrete retaining wall construction conventionally used today is shown in prior art patents. These patents vary in their time frames and in technological sophistication. For example, U.S. Pat. No. 982,698 issued to M. M. Upson is a 1911 patent addressing early concrete retaining wall construction. As is set forth in this reference, such retaining walls are used for docks, railroad embankments, bridges, etc., where dirt, rock or fluids need to be retained. U.S. Pat. No. 1,702,610 teaches a generally T-shaped retaining wall member whose top wall surface gradually increase in height along the rearwardly extending embedment beam. A more recent innovation is set forth and shown in U.S. Pat. No. 4,684,294, issued to O'Neil. This 1987 patent teaches another generally T-shaped cast concrete construction element having a face panel and orthogonally disposed soil embedment beam extending rearwardly therefrom and integrally formed with the face panel. Means are specifically provided for increasing the frictional resistance with the soil mass by sloping the rear wall of the embedment beam.
The above referenced patents describe retaining wall members of the gravity wall type. Other examples of gravity wall type retaining wall members are set forth and shown in several U.S. patents including U.S. Pat. No. 4,196,161, a more recent patent teaching a method for producing pre-cast monolithic concrete units with spaced apart, generally parallel walls and at least one interconnecting beam or cross member. This construction forms a generally "H" shaped member with a frontal member of substantially planar construction disposed in generally parallel spaced relationship to the rear member. U.S. Pat. No. 4,380,409 is a 1983 patent teaching a crib block for erecting bin walls. A unitary pre-cast component comprises a pair of spaced sidewalls having a central connector arm extending therebetween. The unit is constructed with the transverse thickness of the sidewalls and merger segments increasing toward the transverse center line of the unit to increase the resistance to transverse bending loads. The structural elements are shown to be provided in a plurality of lengths, longer lengths being presented at the bottom to accommodate greater forces and shorter lengths being disposed atop a stacked array. Means are provided for interlocking concrete facing panels of each structure and the pre-cast concrete blocks are said to be usable for space barriers, sound barriers, retaining walls, sea walls, dams, flood control walls, bridge abutments and the like.
Another type of retaining wall is that referred to in the industry as the soil reinforced system. These retaining wall structures also utilize a concrete face of generally planar construction, but the face is secured to the tie-back elements embedded in the soil. The tie-back elements are laid within the soil mass as the wall is constructed, and the soil mass directly provides the reinforcement to the retaining wall structure. These structures are generally more economical due to the fact that less concrete is utilized in their fabrication, they are lighter in weight and easier to ship and handle. Tie-back elements do, however, require a greater distance behind the face panel for securement than the gravity wall. A gravity wall member incorporates the weight of the embedment beam as well as the weight of the soil immediately thereabove for securement. For this reason, a great distance behind the face panel is not required for its securement. Distance is, unfortunately, often a major consideration when building retaining walls next to hills and in a limited right-of-way.
A retaining wall is very often provided in a region adjacent a hill or other sloping earthen area. In such a region, the base of the retaining wall near the slope will have a limited distance in which to provide securement of the face panels. However, the base of the retaining wall is the region which receives the greatest loading from the earthen mass which it retains. For this reason, soil reinforced retaining wall systems are not always feasible in applications with limited rearward extension distance. Even retaining walls of limited height have limitations as to the minimal amount of anchoring that is necessary for ultimate stability. When soil reinforcement retaining wall systems are used, the limitation in back depth thus becomes a limitation in the height of the wall. Such problems are not typical of gravity wall systems, which are capable of providing the requisite anchoring force by the concrete embedment beams extending therebehind. However, the advantages of soil reinforcment could be utilized if consideration was given to establishing a greater back depth.
The present invention provides an advance over the prior art by providing a retaining wall system incorporating the advantages of both gravity wall and soil reinforcement walls. The gravity wall is used in the lower region of the retaining wall where maximum force must be accommodated and minimum rear extension distance is usually found. The soil reinforcement members are mounted above the gravity wall system in a region where the loading is reduced, less rearward extension length is required, and more distance is generally available. In this manner a less expensive retaining wall assembly can be utilized with the same structural integrity as a wall system constructed soley of gravity wall members.